By now, surely there are few of us who don’t know the meaning of the following three letters: UPF.

They stand, of course, for ultra-processed food – generally defined as a food wrapped in plastic, containing ingredients you wouldn’t find in your kitchen. They’ve been at the centre of controversy about their detrimental impact on our health.

However, as a women’s health writer and campaigner, I couldn’t help but notice discussions about UPF were almost always generalised in terms of the impact on ‘people’s’ health.

And as we know from other areas of medical research, male ‘people’ are often treated as the default. So I found myself wondering: What about women?

This thought provoked me so much I’ve written a new book analysing precisely how UPF affects women’s bodies. It turns out UPF can wreak a unique toxic havoc on female biology.

For example, every pregnant woman knows to avoid blue cheese because of the small risk of listeria. Yet scientists have discovered high UPF consumption while pregnant can potentially double the risk of miscarriage (more on this later).

UPF, too, has been implicated in everything from ovarian cancer to autoimmune illnesses such as rheumatoid arthritis (and we know that women make up 80 per cent of autoimmune diagnoses).

Some researchers believe high UPF consumption can make menopause symptoms worse, and result in your HRT being less effective. Still, this field remains under-researched and women are not warned about their risk from UPFs.

So why does UPF affect women in such specific ways?

Part of it is down to something scientists are now calling the ‘microsexome’.

UPF is known to be bad for our gut microbiome – the community of bacteria and other microbes in our gut – with a resulting negative impact on our health.

This is in part due to the whole foods that we miss out on when we fill up with UPF: our good bacteria thrive on fibre, found in whole food but distinctly lacking in most UPF.

As well as this, studies suggest additives typically found in UPF – such as emulsifiers, sweeteners, maltodextrin and xanthan gum – could be at best altering, and at worst harming, the microbiome, according to a 2024 review of studies in the journal Nature Reviews.

But, as well as our gut, we now know there are bacterial communities all over our bodies – on our skin, in our urinary system, in our eyes, in our lungs, and, if we are female, in our vagina and reproductive tract.

In a field that currently has more questions than answers, the bacterial colonies in areas of the body unique to women are perhaps the least understood.

But when it comes to the gut microbiome, we know sex plays a role, with scientists now exploring the differences between ‘male’ and ‘female’ microbiomes, known as the microsexome.

Put simply, the sex hormones oestrogen and testosterone – which women and men have in different concentrations – affect the bacteria in our gut. 

This, in turn, influences the metabolism of those sex hormones, a cycle on repeat that appears to be present from very early on, possibly even birth: a 2020 study published in the journal Microbial Cell Factories found these differences are present far before puberty, at which point they intensify.

One area of the microsexome is the ‘oestrobolome’, the collection of bacteria in our gut capable of metabolising and maintaining optimal oestrogen levels.

While men have one too, an oestrobolome that’s functioning optimally is vital for women’s health. The oestrobolome functions best with the help of a healthy gut microbiome – which is not, as we’ve established, aided by UPF consumption.

If your oestrogen levels are too high, you can experience a range of issues, from endometriosis to cancer. Indeed, research published in the Lancet in 2023 which followed nearly 200,000 people found that – even when adjusting for other risk factors, such as smoking – every 10 per cent increase in UPF consumption was associated with a 6 per cent increase of dying from cancer of any kind.

This risk was noticeably higher for women’s cancers: with each additional 10 per cent increase in UPF consumption, there was a 16 per cent increase in the risk of dying from breast cancer and a 30 per cent increased risk of dying from ovarian cancer (both conditions are driven by oestrogen).

You could argue women are uniquely primed to be victims of the UPF industry, particularly when you consider UPF is now thought by some to be addictive. UPFs are deliberately designed to be ‘hyperpalatable’.

Little wonder, perhaps, that these kinds of foods are also causing a unique new kind of addiction – ‘ultra-processed food addiction’ – and, say US psychologists, a unique new kind of eating disorder, ‘ultra-processed food use disorder’. And studies – including one in the journal Nutrients in 2014 – show women are significantly more likely to develop a food addiction than men.

Reaching for UPF when you are unhappy or emotional has a powerful effect on the brain’s reward system, in similar ways to smoking or substance abuse. And this effect may be more pronounced in women (see box).

One of the major points when the impact of UPF on our health can be seen is the moment a girl becomes a ‘woman’ – her first period, or menarche.

A question I am often asked – as the author of a health book for pre-teen girls about puberty – is why girls appear to be getting their periods younger (between the age of eight and 13 generally), along with the first signs of puberty, such as breasts and pubic hair.

An early start to puberty can not only be distressing, but has also been linked to mental health issues and a slightly increased risk of breast cancer later in life.

It’s a complex subject, but it’s possible UPF is driving this downward trend.

We know UPF is a big factor in obesity and researchers have shown higher BMI can trigger earlier puberty.

One of the key hormones involved is kisspeptin. If you have more fat cells, you produce more of another hormone called leptin – and leptin then promotes the release of kisspeptin, triggering puberty. That said, it’s not quite so straightforward. One Harvard study from 2015 found that girls who consume lots of ultra-processed drinks with added sugar, such as sodas and energy drinks, are likely to start their periods earlier – even when their BMI is lower.

A more recent study in 2022, published in the journal Frontiers in Public Health, also found that consuming probiotic yoghurt – which contains live bacteria for gut health – mitigated the fizzy drink effect on menarche, suggesting the microbiome may be involved.

And a 2020 study of more than 1,000 girls in China found those who consumed lots of fast foods and not much fibre were 33 per cent more likely to experience early periods. Interestingly, this was independent of their BMI.

While heavy or painful periods are often dismissed as the ‘luck of the draw’, there are potential links to UPF here, too.

Menstrual cramps and heavy periods can be caused by high levels of hormone-like compounds called prostaglandins. Another factor can be high oestrogen in relation to progesterone, sometimes called ‘oestrogen dominance’.

Those pain-inducing high prostaglandin levels can also be a response to inflammation, which numerous studies – including one last year from the University of California – have linked to UPF.

Some researchers have even labelled this inflammation ‘fast-food fever’, suggesting the body might not recognise UPF as food and so mounts an inflammatory response against it.

Indeed, two separate studies – one in the International Journal of Food Sciences and Nutrition in 2009, the other in the journal BMC Women’s Health in 2018 – both conducted before the term UPF was coined, looked at dietary patterns of women in relation to period pain and found those eating high levels of snacks and junk food were more likely to have painful periods.

Endometriosis – a condition where cells similar to those lining the womb grow elsewhere, causing chronic pain and, in some cases, fertility issues – has similar associations with UPF.

Researchers have found differences in the gut, vaginal and endometrial microbiomes of women with endometriosis and a number of studies, like one published in 2023 in the journal Frontiers in Nutrition, have shown diet – eating less red meat and trans fat (found in pastries, cakes and biscuits under names like ‘hydrogenated fat’), and more plant-based fibre – could improve the condition.

It was perhaps most shocking to discover the potential impact high UPF consumption could have during pregnancy. 

A large-scale analysis by the University of Birmingham in 2023, of data from over 63,000 women, found that a diet high in UPF was associated with double the risk of miscarriage – but a high intake of fruit and vegetables saw a similar risk reduction. 

It’s thought to be due to the vitamins and minerals women lack when their diet is high in UPF.

Two separate studies have also found eating high levels of UPF in what is called the ‘periconceptional period’ – the time from shortly before you get pregnant and into the pregnancy itself – is associated with smaller embryo growth. One theory is that nutrient deficiency on a UPF diet affects overall skeletal development.

Every single autoimmune condition is more prevalent in females. For instance, Sjogren’s syndrome, which affects parts of the body that produce fluids - causing dryness - has a female to male ratio of 19:1.

Scientists are still trying to understand these disorders, which began rising globally around four decades ago.

But James Lee, a world expert in autoimmune disorders based at the Francis Crick Institute in London, pointed to UPF consumption, telling me: ‘We don’t know specifically what’s changed in the last 40 years that has caused a rise in autoimmune diseases, and it’s likely a combination of factors – pollution, obesity, stress, early-life antibiotics, infections – but our Western diet is probably a contributing factor.

‘For example, emulsifiers in our food could thin the protective mucus in our guts and bring our microbiomes into direct contact with our immune systems.’

The immune system can overreact, potentially leading to autoimmune conditions.

Several studies have shown a link between high consumption of UPF and inflammatory bowel disease (IBD), for instance, with particularly strong findings for Crohn’s disease, the type of IBD women are most likely to have.

Other research found that women with fibromyalgia, a disorder that causes pain and tenderness all over the body, reported an improvement in symptoms after a three-month anti-inflammatory diet that included cutting out UPF.

The scale of potential issues for women’s health linked to UPF is almost overwhelming. It’s almost as mind-boggling as the scale of UPF production itself – on a single day in the UK alone, factories churn out 12 million loaves of bread and 10 million cakes and biscuits. That’s an awful lot of UPF – and shows just how vital it is that all of us, especially women, kick our addiction.

WHY FEMALE BRAIN CRAVES SWEET TREATS

Could women be particularly vulnerable to UPF’s harms? Our brains seem to be different in areas connected to appetite regulation and energy maintenance – suggesting what drives us to overeat is different.

Researchers studying male and female brains found obese women showed more prominent changes in the brain’s reward system related to dopamine – a chemical messenger known as the ‘feel-good’ hormone – suggesting emotion-related eating and compulsive eating played a larger role for them.

But the team from the University of California discovered that obese men’s brains showed more triggers in sensorimotor regions – which control movement, and process touch and sensation – possibly meaning they overeat as they’re drawn to the physical sensation of UPF. 

Numerous other studies have concluded women are more likely than men to turn to food for comfort when stressed, angry or depressed.

And we all know the food women turn to is very likely to be UPF – chocolate, crisps, ice cream. I mean, when was the last time you stress-ate a banana?

HOW FIZZY DRINKS AND SAUSAGES COULD MAKE MENOPAUSE MORE INTENSE 

While researching this subject, I was struck by how, through all our life phases, women are readily given the option of being medicalised. This is sometimes necessary or even life-saving.

But our perception of the female body as inherently faulty causes us to lean too heavily on this option, blinding us to the possibility that health issues may not just be part of the dreadful package of being female, but exacerbated – or even caused – by factors that are within our capacity to change.

This is especially pertinent during the menopause. As Joyce Harper, a professor of reproductive science at University College London, told me: ‘The impact of diet and lifestyle on menopause is totally under-discussed. HRT has a place, but should be seen as just one tool in the menopause toolkit.’

And the research is pretty clear: avoiding UPF and eating a Mediterranean-style diet of mostly plants will have an impact on your menopause experience, and even on the effectiveness of HRT.

One 2022 study by the University of Sao Paulo in Brazil found the highest level of UPF consumption was associated with more intense hot flushes and night sweats. Quite specifically, those regularly consuming sugar-sweetened drinks and eating sausages were most likely to suffer the physical symptoms

of the menopause, as well as having issues related to memory and concentration.

Those in the study eating less UPF and more vegetables, on the other hand, reported being less affected.

The cherry on the UPF cake for menopausal women perhaps comes from a 2023 study of 119 females in the US.

This suggested those who were obese – a condition linked to high UPF consumption – may not only have worse symptoms of menopause, but find their HRT less effective. The study authors speculated that this may be because of the impact of BMI on drug metabolism.

• Adapted from Ultra-Processed Women by Milli Hill (HQ, £16.99), to be published 3 July. © Milli Hill 2025. To order a copy for £15.29 (offer valid to 01/07; UK P&P free on offers over £25) go to mailshop.co.uk/books or call 020 3176 2937.